The subject species, Holothuria scabra is a widespread Indo-Pacific species. It occurs in Asia, Australia and Madagascar in the Indian Ocean in sandy, shallow-water, eel grass beds. Presence below indicated by yellow...

Its a pretty neat beast. It can actually BURY itself into the sandy substrate. Presumably, it is this aspect which earns it, the common name the "SANDFISH". Yes, if you thought "starfish" was bad.."Sandfish" is even worse and will make your broil in your juices!

The STUDY
Wolkenhauer et al., undertook their study in Moreton Bay, in south-east Queensland in Australia in 2003 and 2004. The authors tested the presence/absence/density of H. scabra relative to its surroundings.

They caged areas off and separated places where cukes were either present/excluded/ Or impeded by the cages. The authors are careful to note that their study was potentially affected by the time of the year and the number of replicate times they performed the study...but the outcome and its impact remains important.

The RESULTSThe short version is: Removing sea cucumbers AFFECTS SEA GRASS systems. In the words of the authors: "seagrass systems may suffer in the absence of holothurians..."

Now, for the sake of space, I'm not going to include EVERY little bit of uncertainty and statistical variation in the data but I will boil it down and say that while there is still DOUBT, there is definitely some signal that suggests exclusion of sea cucumbers from an area will affect seagrass productivity. but here are some choice bits...Losing Seagrass....
Here is their Figure 3, which shows the two experiments showing average seagrass productivity during the 2003 and 2004 experiments. In this particular experiment examining seagrass biomass there has been a significant decrease over the study period when the cucumbes are REMOVED.So, what is it about sea cucumbers that makes sea grass beds THAT much more productive when cukes are around??

By ingesting all that sediment and sand and burying itself in the sediment, this kicks up all of the good organic food into the water and can knock loose food and nutrients that would be usable by the seagrass bed and other nearby plants and organisms.

Seagrass beds might also be taking advantage of sea cucumber "ammonium excretions" (which some humans would call "pee" but I would not) into the local ecosystem., thus feeding the surrounding plants and animals.

How much affect would this have??

This paper is one of the foundations of understanding how this "nutrient cycle" could work..

There are other studies in subtropical settings which show that algae and bacterial production is REDUCED when sea cucumbers are GRAZING. Up to 10 to 40% of bacterial carbon produced in the summer is apparently taken by sea cucumbers.

This is conceivably a HUGE impact on the productivity of a region!! With the cukes gone, who eats the bacteria????

The full impact of this hasn't been totally explored but just some hypotheticals you may be familiar with-What happens in your aquarium tank when you've got too much nutrients and bacteria again???? Your nutrient balance is out of whack. Think of your stomach suddenly producing too much gas. Or a lake with too much algae.Conclusions: What Do We Take Away from This?

There is a logical chain of events/implication from Wolkenhauer's results.

Sea cucumbers are part of the "natural filtration" function that seagrass beds serve in marine ecosystems.

By burying themselves and freeing up the sediment, they encourage other ecological interactions around them which causes the flow of nutrients and so on.

REMOVAL of sea cucumbers from this system through destructive overfishing, could conceivably harm the seagrass bed/seagrass systemAnd why save sea grass?

Well, for one thing, other commercially fished FISH and many other species live there. But they serve to filter nutrients and chemical inputs to the marine environment among other reasons. which can be found at Sea grass Watch.org. But to boil it down: Seagrass beds are ecologically IMPORTANT.

Removal of just this ONE species, H. scabra showed an impact on the system.

Could the lowly sea cucumber could potentially be the ecological lynchpin to the ecological health of seagrass beds??

Thursday, June 24, 2010

BREAKING NEWS!Wouldn't it be cool if US news found freakish square shaped starfish newsworthy?Patiria pectinifera is the Japanese sister species to the Pacific Northwest Patiria miniata.. here, we see the ANN News channel reporting on this "strange" (although its really not that unusual) irregularity!

Honestly, though? I have no idea what they are saying. If anyone can provide a translation it would be greatly appreciated!!

and to round out the weekend... here is Japanese super hero Kamen Rider V3 fighting RAZOR STARFISH!!!! (yeah its no Starfish Hitler, but what is?)

So, owing to various distractions, including a mild bout of food poisoning this week has been kind of light!

Here's some Pacific Northwest starfish videos that always seem to be popping up on YouTube!I've actually been wondering why it is there's so MANY videos from the Pacific Northwest relative to Australia and New Zealand, which has a comparably diverse fauna. C'mon guys! show me some starfish (or other echinoderm) lovin!!

1. Dermasterias and the escape response it illicits from Sea anemones. This video escaped me earlier because its listed under "swimming sea anemones" (hmpf!)... I blogified a little bit about this here..

2. Some Bat Star (Patiria miniata) time lapse!

3. What happens when you leave Henricia high and dry? It moves back underwater...but you'd never see it...

4. And here's a nice intro w/ great footage to the Sunflower star (Pycnopodia helianthoides) from the west coast of North America!

The subject of our story, is a multi-armed starfish, Heliaster microbrachius whose living members are found in the East Pacific (South & Central America).In fact, Heliaster is part of a species complex (a cluster of closely related species present in a discrete geographic range) throughout this region and different variable body forms can be encountered on the Pacific side from Mexico to Central America to Chile. Effectively, Heliaster is ONLY found in this part of the world.

Here are some photos from the oral surface (the underside) of a living Heliaster for comparison...

...with the surface of the fossil! The details are amazingly well preserved! Its not often you can identify a fossil starfish to species with confidence.The specimens (apparently over 360 were collected) were exceptionally well preserved, so well preserved they were able to positively identify it as Heliaster microbrachius, a species that continues to be around even today.

That would mean that this species at one time, woudl have lived from Florida ALL the way to Mexico/Central America and along the "Pacific" coast!!WHAT? But how does THAT make sense? For something from the PACIFIC to be found SO FAR away from where the living ones are found?? How did that happen?

To understand this little mystery..let's learn a little interesting geology about Central America...

North and South America are connected by a narrow strip of land called the Isthmus of Panama.

(from Wikipedia)

But the Panamanian isthmus was NOT ALWAYS THERE. and that's important to know.

Its formation is considered by some to be one of the most important geological events of the last 60 million years, in part because its formation, triggered glaciation in the Arctic-among other reasons which I'll outline below.

It was essentially an OPEN channel, called the Central American Seaway through which an ocean current traveled connecting the "Atlantic" with the Pacific Ocean. Bear in mind, that also means that there was LIFE here. And it was connected ACROSS the Central American Seaway.

Over time, tectonics triggered uplift and formation of the isthmus-effectively BLOCKING currents from flowing through the seaway that had been there before.

This blockage essentially CREATED the modern day Gulf Stream and led to glaciation of the Arctic. You can see the complete story at the WHOI website..but the current flow below shows this very nicely...

But a bridge for the land-critters is a BARRIER for marine organisms.
Based on the fossil deposits (2.2-2.5 million years) and the age of the land bridge, the authors bracket the age of the Heliaster fossil at about 2.5-3.5 Million years ago.. suggesting that it might have been present well AFTER the land bridge sealed off the populations between the Pacific and Atlantic.

There is a fairly sizeable fauna of mollusks and other invertebrates that are also found as part of the fossil deposit where this species was found. These all point towards continuity BETWEEN the populations in the "East Pacific" (Mexico, Central America, etc.) and Florida about 2-3 million years ago.

So, the land bridge formation was a kind of "starfish natural disaster" of sorts- as it cut off this small population of this species from the rest..and the subsequent changes in the marine environment likely led to their localized extinction.

If you look at the entry for bat stars in any intertidal guide to marine invertebrates, the range for this species is reliably cited as "Southern California up to British Columbia and Alaska..."But what often gets left out, is that there's a strange disjunction or absence of these starfish along a segment of the coast between Oregon and Washington! The first step was to look at the genetic relationships between the bat stars along the coast.Is the disjunction the start of new distinct species (i.e., isolated populations) ?? We've seen this kind of method applied in a previous post about the color morphs of Pisaster (see here).

The authors extracted DNA from 423 individuals from 14 locations from Alaska, the Queen Charlotte Islands, Vancouver Islands, and California (from Fort Bragg to Santa Barbara).DNA from these specimens can be analyzed and compared so that they essentially assess the overall similarity between them and among them. Plus, they can use DNA to determine how the genetic material of the sampled animals flows between and among populations. They can boil this down to a hand-dandy intuitive diagram that shows where the genetic populations of bat stars on the Pacific Northwest coast occur relative to one another...

(Fig. 1 from Keever et al., 2009)

The circles represent the samples taken. The larger size of circles represents the number of specimens sampled. The colors correspond to distinct haplotypes (the aforementioned genetic material) from each original region. Thus, red corresponds to specimens originally from California, green from Vancouver, and blue from Alaska/northern Haida Gawaii (in the northern part of the Queen Charlotte Islands). Each circle (i.e. the samples) has multiple colors, suggesting some mixing of populations in each region. You can see distinctly different colors (i.e., the haplotypes) between the more northern populations [i.e., blue from Alaska and North Vancouver (Haida Gawaii)] versus the red/green/blue populations in the southern regions (California and Vancouver Island).

The genetic "break" between the Northern populations versus the Southern populations may have been caused by past oceanographic barriers, such as the west to east North Pacific Current.The North Pacific Current may form a barrier to the larval forms of this species as it effectively keeps the two populations apart..On the other side of the range...Based on the data on gene flow, it turns out there's a LOT of genetic mixing between southern populations, especially between California and southern Vancouver.

(modified Fig. 3 from Keever et al., 2009)

So, what do we know about the OR/WA disjunction??There was no direct evidence that these genetic populations showed isolation or the beginning of distinct species across the Washington/ Oregon Disjunction (i.e., the no bat star zone). In fact there was 10 TIMES higher the rate of gene flow across the range disjunction relative to the gene flow in the Queen Charlotte Sound.(Note that a high rate of gene flowgenerally suggests coalesence of a population rather then a separation).

Unfortunately for this idea-the genetic structure of Patiria miniata populations don't match up with the disjunction.

Without a clearer explanation, the authors can only speculate that there was a "recent local extirpation" which would have broken up Patiria's range along the coast....perhaps something more ecological then historical or geological. At this point, the Washington-Oregon disjunction remains a matter of "well, we know its not that..."But stay tuned! you never know what will come up next!

Tuesday, June 1, 2010

The giant Indo-Pacifc sand star Luidia maculata...in life and then disturbed, turned over and then, righting itself. This one is pretty amazing .....

This week is a short week because of Memorial Day on Monday and various other factors have conspired against me! So..today is videos of GIANT multi-armed starfish from various places TURNING themselves over!!

For some reason, people are always fascinating watching starfish do this! WHY? I don't know. But for some reason its better when the animals are huge, multi-armed freakish starfish monsters!!! GO!Here's Coscinasteriascalamaria from Australia...

About Me

I pursue starfish related adventure around the world with a critical eye and an appreciation for weirdness.
Support has been courtesy of the National Science Foundation but the views and opinions presented herein are mine and do not reflect the opinions of them or any affiliated institutions.
Need to hire an invertebrate zoologist/marine biologist? Please contact me!